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Agronomist says: Forage sorghum silage stacks up against corn

As aquifers across the Southwest and Delta dry up, researchers are rushing to find solutions to stave off disaster. This means a focus not only on replenishing the water supply, but field work as well.

“A lot of agriculture acres just can't be irrigated anymore,” says Brent Bean, an agronomist with Texas A&M. “We certainly can't grow corn in as many areas as we used to. Alternative crops are something everyone is looking at.”

With more feed yards and dairies moving into the Southwest, a greater market for silage and hay has sprung up. If, in some areas, producers don't have the water to grow corn silage (what feed yards tend to prefer) what will be the alternative? What will be grown in corn silage's place?

Bean, who spoke at the 2004 Sorghum Industry Conference in Little Rock, says forage sorghum silage is a good choice. Bean's research shows the crop can grow on about 40 percent less water than corn requires. And even with less water, the forage sorghum can achieve yields comparable to corn.

Bean and colleagues first started testing forage sorghums in 1999 at the request of the Texas Seed Trade Association. Since then, the effort has grown. Last year, over 90 entries were entered in Bean's forage sorghum variety trials conducted outside Amarillo at the Bushland Texas Agricultural Experiment Station.

“We get a lot of requests from all over the country regarding our research,” he says. “The data we collect can be used nationwide. We provide yield data, lodging scores, and a complete nutrient analysis. People want that information. I'm unaware of anyone testing as many sorghum varieties in one place.”

In his research, Bean deals with several sorghum types beyond conventionals.

Photo-period sensitive (PS) sorghums respond to day length when switching from a vegetative growth stage to producing grain. PS sorghums may grow 12 feet tall without producing a head. The plants won't head out until the day length gets shorter than around 12 hours and 20 minutes, says Bean. Around the Amarillo area, that's around Sept. 20.

“For us, though, we'll freeze before the head ever emerges from the whorl,” says Bean. “The advantage of the PS sorghums — or sorghum sudans — is they can produce a lot of tonnage. But there's a trade-off: the quality of PS sorghums isn't nearly as good for silage as non-PS sorghums.”

Brown mid-rib (BMR) sorghums on average have less lignin content in the leaves and stalks. Lignin is indigestible for cattle — therefore, the lower the lignin content, the better the digestibility and palatability of the variety.

The problem with BMRs is when you remove lignin from the plants, it weakens them. “It's kind of like taking re-bar out of concrete,” says Bean. “Potentially, this means a farmer could see more lodging with this type of sorghum.”

What a producer wants to use the sorghum silage for helps determine which of these sorghum types to grow, says Bean. “If you're just feeding some cattle through the winter and aren't worried about a lot of gain, then the PS varieties might be the way to go because they'll give you higher tonnage. On the other hand, if you're feeding dairy cattle and need high-quality silage, you'll want to go with a BMR or a higher-quality conventional. The main point is there are certain forage sorghum varieties that are close to corn's quality.”

What about quality issues surrounding forage sorghum?

“Corn provides a good-quality feed, no doubt. Our data is showing some conventional forage sorghums with very good quality — close to corn. There are a number of BMR forage sorghum varieties approaching corn's quality.”

Bean points to a corn/sorghum study of in-season irrigation water use. “In 2001, sorghum average yield was 24.5 tons per acre with corn at 23.8 tons — that's very similar. To get (those results), in-season irrigation was 13.2 inches of water on the sorghum and 28.2 inches on the corn. That's a 53 percent swing in favor of the sorghum.”

It's important to note this water use was in-season. Bean and colleagues put a preseason irrigation on both crops that wasn't figured in. They also didn't consider rainfall in the study.

In 2002, the numbers show that sorghum yields were at 26.9 tons using 14.5 inches of in-season irrigation water. The corn yielded 25 tons and needed 24.6 inches of water — 41 percent more water than the sorghum required.

However, in 2003, again with about 40 percent less water used on the sorghum, there was a shift in yields. Forage sorghums yielded 19.2 tons versus 25.5 tons of corn.

“That's the first year we've seen that happen,” says Bean. “I think it had to do with the heat we had here. It was extremely dry and we ended up putting much more water on the sorghum and corn (22.2 inches and 37.3 inches, respectively). July was very hot and it seemed to hurt sorghum yields more than corn.”

Bean points next to data concerning 2001's irrigated sorghum silage tons produced per inch of irrigation. “This shows that on the 43 forage sorghums, for every in-season inch of irrigation applied, we got 1.87 tons of forage back (at 65 percent moisture). Corn, meanwhile, showed 1 inch of water produced 0.93 ton. Even though they yielded almost the same, it took almost double the water to make the corn. Similar results were observed in 2002.”

In 2003, for every inch of irrigation on forage sorghums, one ton was produced. Corn didn't do well, either: 0.60 ton per inch of water.

In tests conducted from 2000 to 2002 BMR forage sorghums yielded approximately 10 percent less than the conventional forage sorghums. “In 2003, we saw a decrease in BMR yields of about 26 percent. Again, that's the first time we've seen such a drop and suspect it's due to the hot, dry year we just had. The BMRs really don't like that kind of weather.”

IVTD (in-vitro true digestibility) is a measure of the digestibility of a given sorghum. In a 2001 test, Bean found that two of the corn tests were above 85 percent digestibility with two a bit below 80 percent. If corn is the standard for digestibility and quality, “we want sorghums that will favorably compare. This study showed that quite a few BMR forage sorghums' digestibility fall right in with corn. There are a few conventional sorghums that are in line with corn, too. While the (PS) sorghum yield is good, the quality of this type of sorghum is not nearly as good as the corn or other sorghum.”

In 2003, Bean also looked at percent lodging by sorghum type. “When you average it all together, we saw 14.4 percent lodging in BMRs. That's quite a bit more than the 4.2 percent seen in non-BMRs. The distribution of the lodging needs to be paid close attention to, though. Looking at individual varieties, there is a bunch of BMRs at less than 10 percent lodging. Now, there are a few way above that (three listed are over 40 percent), but there are plenty of BMRs that a farmer might want to consider. This is where variety selection is important.”

Bean conducted a study to see if the amount of sorghum lodging could be affected. He tested two varieties: BMR 100 (has a history of lodging) and BMR 106 (stands up well). Bean looked at the effects of seeding rates (30,000; 60,000; 120,000) and nitrogen rates (50 pounds and 100 pounds) in the two varieties.

BMR 106 wasn't bothered — the variety didn't lodge regardless of nitrogen or seeding rate. The BMR 100, though, suffered more lodging as either nitrogen or seeding rates were increased. If a producer wants to grow a variety prone to lodge, suggests Bean, he'll want to be careful not to put too much nitrogen out and go with the lowest seeding rate.

“We also looked at what would happen to sorghum yields if nitrogen and seeding rates are lowered. In fact, in the 2003 study, yields weren't affected. Now, I want to point out we have only one year of data, so I'm not sure if these particular results will hold up every year.”

Does manipulating seeding or nitrogen rates hurt quality? “We didn't see any affect on quality.”

“We get this question all the time: ‘You guys are using full irrigation on these tests, but what will my yields be in a situation that isn't full irrigation?’”

To answer that question, Bean tested four hybrids on four irrigation levels — dryland, 4 inches, 8 inches, and 16 inches. From a research standpoint, data came out very well.

“The yield response to an acre-inch of water was, in this case, very linear. For every inch of water, we got back 0.69 ton of wet silage. We're getting about two-thirds of a ton per acre-inch of water.”